Cooling air is frequently used to cool the materials of the exhaust nozzles used in gas turbine engines. Frequently, fan air is used where considerable pressure is available to direct and modulate the cooling airflow.
In engines with high fan pressure ratios the cooling air is extensively compressed and therefore at an elevated temperature. Accordingly, it is difficult to achieve adequate cooling with this higher temperature air.
It is known therefore, to design the nozzle as an ejector whereby cooling air can be induced at the throat plane. Ambient air enters the ram duct and is induced from there into the nozzle adjacent the surfaces. It can be appreciated that very little excess pressure is available with this arrangement.
When nozzles are used requiring pitch or yaw, a backflow of hot gases occurs into the ejection area before any significant amount of vectoring occurs. It is desirable to eject cooling air in a manner that maintains the flow of cooling air despite vectoring operation of the nozzles.